This is an isosceles triangle:
3x = y + 7
Make y the subject:
y = 3x - 7 ------------------------------------ (1)
Sum of all angles in a triangles is 180:
3x + (y + 7) + 90 = 180
Simplify the equation:
3x + y + 7+ 90 = 180
3x + y = 180 - 90 - 7
3x + y = 83
Make y the subject:
y = 83 - 3x ------------------------------------ (2)
Equate (1) and (2) and find the value of x:
3x - 7 = 83 - 3x
3x + 3x = 83 + 7
6x = 90
x = 15°
Find the value of y:
y = 3x - 7
When x = 15
y = 3(15) - 7
y = 38°
Ans: x = 25°, y = 38°
